diff --git a/.gitmodules b/.gitmodules
index f1b9cf5..a63cbff 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule "Prolog-Library-Collection"]
  path = Prolog-Library-Collection
  url = https://github.com/wouterbeek/Prolog-Library-Collection.git
+[submodule "plHtml"]
+    path = plHtml
+    url = https://github.com/wouterbeek/plHtml.git
diff --git a/Prolog-Library-Collection b/Prolog-Library-Collection
index 4a51c6e..184c33e 160000
--- a/Prolog-Library-Collection
+++ b/Prolog-Library-Collection
@@ -1 +1 @@
-Subproject commit 4a51c6e0936179bff57fda23686219e6a6cd3c9b
+Subproject commit 184c33eecf561c109919a7f765de0b1e53d99d00
diff --git a/plHtml b/plHtml
new file mode 160000
index 0000000..2c45ebc
--- /dev/null
+++ b/plHtml
@@ -0,0 +1 @@
+Subproject commit 2c45ebcd3f946c1e207a69ece1e2d730d4d090ed

diff --git a/Prolog-Library-Collection b/Prolog-Library-Collection
index 184c33e..03d4b46 160000
--- a/Prolog-Library-Collection
+++ b/Prolog-Library-Collection
@@ -1 +1 @@
-Subproject commit 184c33eecf561c109919a7f765de0b1e53d99d00
+Subproject commit 03d4b46ba9c6f658828ff843e5785c221ffc3a57
diff --git a/plHtml b/plHtml
index 2c45ebc..50743da 160000
--- a/plHtml
+++ b/plHtml
@@ -1 +1 @@
-Subproject commit 2c45ebcd3f946c1e207a69ece1e2d730d4d090ed
+Subproject commit 50743daad8dd0f3664e1cafbc14523a423314f84

diff --git a/gv_attr_type.pl b/gv_attr_type.pl
index c62d146..200c034 100644
--- a/gv_attr_type.pl
+++ b/gv_attr_type.pl
@@ -41,7 +41,7 @@
   ]
 ).
 :- reexport(
-  gv(gv_color),
+  plGraphViz(gv_color),
   [
     color//1, % +Color:compound
     colorList//1 % +ColorList:list(compound)
diff --git a/gv_attrs.pl b/gv_attrs.pl
index 81d51df..728640e 100644
--- a/gv_attrs.pl
+++ b/gv_attrs.pl
@@ -68,7 +68,7 @@ check_minimum(V, Min1):-

 gv_attrs_download:-
   gv_attrs_url(Url),
-  download_html(Url, Dom, [html_dialect(html4)]),
+  download_html(Url, Dom, [html_dialect(html4),verbose(silent)]),

   xpath(Dom, //table(@align=center), TableDom),
   % @tbd This does not work, since in `record_name(Element, Name)`,
diff --git a/gv_color.pl b/gv_color.pl
index fd22d35..ad18728 100644
--- a/gv_color.pl
+++ b/gv_color.pl
@@ -81,7 +81,7 @@ gv_color_url('http://www.graphviz.org/doc/info/colors.html').

 gv_color_download:-
   gv_color_url(Url),
-  download_html(Url, Dom, [html_dialect(html4)]),
+  download_html(Url, Dom, [html_dialect(html4),verbose(silent)]),
   xpath(Dom, //table(1), TableDom1),
   xpath(Dom, //table(2), TableDom2),
   maplist(assert_color_table, [x11,svg], [TableDom1,TableDom2]).

diff --git a/gv_attrs.pl b/gv_attrs.pl
index 728640e..b360039 100644
--- a/gv_attrs.pl
+++ b/gv_attrs.pl
@@ -14,16 +14,21 @@
 */

 :- use_module(library(apply)).
+:- use_module(library(persistency)).
 :- use_module(library(xpath)).

 :- use_module(dcg(dcg_content)).
 :- use_module(dcg(dcg_generic)).
+:- use_module(generics(db_ext)).
+:- use_module(os(file_ext)).

 :- use_module(plHtml(html)).
 :- use_module(plHtml(html_table)).

 :- use_module(plGraphViz(gv_attr_type)). % DCGs implementing attribute types.

+:- db_add_novel(user:prolog_file_type(log, logging)).
+
 %! gv_attr(
 %!   ?Name:atom,
 %!   ?UsedBy:list(oneof([cluster,edge,graph,node,subgraph])),
@@ -33,9 +38,18 @@
 %!   ?Notes:atom
 %! ) is nondet.

-:- dynamic(gv_attr/6).
+:- persistent(
+  gv_attr(
+    name:atom,
+    used_by:list(oneof([cluster,edge,graph,node,subgraph])),
+    types:list(atom),
+    default,
+    minimum,
+    notes:atom
+  )
+).

-:- initialization(gv_attrs_download).
+:- initialization(gv_attrs_init).



@@ -64,7 +78,20 @@ check_minimum(V, Min1):-



-% Download attributes from graphviz.org
+% INITIALIZATION
+
+%! assert_gv_attr_row(+Row:list(atom)) is det.
+
+assert_gv_attr_row([Name,UsedBy1,Types1,Default1,Minimum,Notes]):-
+  dcg_phrase(translate_usedby(UsedBy2), UsedBy1),
+  once(dcg_phrase(translate_type(Types2), Types1)),
+  sort(UsedBy2, UsedBy3),
+  translate_default(Default1, Default2),
+  assert_gv_attr(Name, UsedBy3, Types2, Default2, Minimum, Notes).
+
+
+%! gv_attrs_downloads is det.
+% Downloads the table describing GraphViz attributes from `graphviz.org`.

 gv_attrs_download:-
   gv_attrs_url(Url),
@@ -76,16 +103,56 @@ gv_attrs_download:-
   %%%%xpath(Dom, /html/body/table, TableDom),

   html_to_table(TableDom, _, Rows),
-  maplist(assert_gv_attr, Rows).
+  maplist(assert_gv_attr_row, Rows).
+
+
+%! gv_attrs_file(-File:atom) is det.
+
+gv_attrs_file(File):-
+  absolute_file_name(
+    data(gv_attrs),
+    File,
+    [access(write),file_type(logging)]
+  ).
+
+
+%! gv_attrs_init is det.
+
+gv_attrs_init:-
+  gv_attrs_file(File),
+  safe_db_attach(File),
+  file_age(File, Age),
+  gv_attrs_update(Age).
+
+
+%! gv_attrs_update(+Age:float) is det.
+
+% The persistent store is still fresh.
+gv_attrs_update(Age):-
+  once(gv_attr(_, _, _, _, _, _)),
+  Age < 3600, !.
+% The persistent store has become stale, so refresh it.
+gv_attrs_update(_):-
+  retractall_gv_attr(_, _, _, _, _, _),
+  gv_attrs_download.
+
+
+%! gv_attrs_url(-Url:url) is det.

 gv_attrs_url('http://www.graphviz.org/doc/info/attrs.html').

-assert_gv_attr([Name,UsedBy1,Types1,Default1,Minimum,Notes]):-
-  dcg_phrase(translate_usedby(UsedBy2), UsedBy1),
-  once(dcg_phrase(translate_type(Types2), Types1)),
-  sort(UsedBy2, UsedBy3),
-  translate_default(Default1, Default2),
-  assert(gv_attr(Name, UsedBy3, Types2, Default2, Minimum, Notes)).
+
+%! safe_db_attach(+File:atom) is det.
+
+safe_db_attach(File):-
+  exists_file(File), !,
+  db_attach(File, []).
+safe_db_attach(File):-
+  touch_file(File),
+  safe_db_attach(File).
+
+
+%! translate_default(+Default1:atom, -Default2:atom) is det.

 % The empty string is represented by the empty atom.
 translate_default('""', ''):- !.
@@ -93,12 +160,20 @@ translate_default('""', ''):- !.
 translate_default('<none>', _):- !.
 translate_default(Default, Default).

+
+%! translate_type(-Types:list(atom))// is det.
+
 translate_type([H|T]) -->
   {gv_attr_type(H)},
   atom(H),
   whites,
   translate_type(T).
-translate_type([]) --> [].
+translate_type([]) --> !, [].
+
+
+%! translated_usedby(
+%!   -UsedBy:list(oneof([cluster,edge,graph,node,subgraph]))
+%! )// is det.

 translate_usedby([cluster|T]) --> `C`, !, translate_usedby(T).
 translate_usedby([edge|T]) --> `E`, !, translate_usedby(T).
diff --git a/gv_color.pl b/gv_color.pl
index ad18728..cf92f56 100644
--- a/gv_color.pl
+++ b/gv_color.pl
@@ -18,20 +18,25 @@

 :- use_module(library(apply)).
 :- use_module(library(lists)).
+:- use_module(library(persistency)).
 :- use_module(library(xpath)).

 :- use_module(dcg(dcg_abnf)).
 :- use_module(dcg(dcg_cardinal)).
+:- use_module(generics(db_ext)).
+:- use_module(os(file_ext)).
 :- use_module(sparql(sparql_char)).

 :- use_module(plHtml(html)).
 :- use_module(plHtml(html_table)).

+:- db_add_novel(user:prolog_file_type(log, logging)).
+
 %! gv_color(?Colorscheme:oneof([svg,x11]), ?Color:atom) is nondet.

-:- dynamic(gv_color/2).
+:- persistent(gv_color(colorscheme:oneof([svg,x11]),color:atom)).

-:- initialization(gv_color_download).
+:- initialization(gv_color_init).



@@ -75,9 +80,9 @@ wc_weight(Float) -->



-% Initialization.
+% INITIALIZATION

-gv_color_url('http://www.graphviz.org/doc/info/colors.html').
+%! gv_color_download is det.

 gv_color_download:-
   gv_color_url(Url),
@@ -91,6 +96,52 @@ assert_color_table(Colorscheme, TableDom):-
   append(Rows, Cells),
   forall(
     member(Cell, Cells),
-    assert(gv_color(Colorscheme, Cell))
+    assert_gv_color(Colorscheme, Cell)
+  ).
+
+
+%! gv_color_file(-File:atom) is det.
+
+gv_color_file(File):-
+  absolute_file_name(
+    data(gv_color),
+    File,
+    [access(write),file_type(logging)]
   ).

+
+%! gv_color_init is det.
+
+gv_color_init:-
+  gv_color_file(File),
+  safe_db_attach(File),
+  file_age(File, Age),
+  gv_color_update(Age).
+
+
+%! gv_color_update(+Age:float) is det.
+
+% The persistent store is still fresh.
+gv_color_update(Age):-
+  once(gv_color(_, _)),
+  Age < 3600, !.
+% The persistent store has become stale, so refresh it.
+gv_color_update(_):-
+  retractall_gv_color(_, _),
+  gv_color_download.
+
+
+%! gv_color_url(-Url:url) is det.
+
+gv_color_url('http://www.graphviz.org/doc/info/colors.html').
+
+
+%! safe_db_attach(+File:atom) is det.
+
+safe_db_attach(File):-
+  exists_file(File), !,
+  db_attach(File, []).
+safe_db_attach(File):-
+  touch_file(File),
+  safe_db_attach(File).
+

diff --git a/gv_attrs.pl b/gv_attrs.pl
index b360039..fa499d0 100644
--- a/gv_attrs.pl
+++ b/gv_attrs.pl
@@ -130,7 +130,7 @@ gv_attrs_init:-
 % The persistent store is still fresh.
 gv_attrs_update(Age):-
   once(gv_attr(_, _, _, _, _, _)),
-  Age < 3600, !.
+  Age < 8640000, !.
 % The persistent store has become stale, so refresh it.
 gv_attrs_update(_):-
   retractall_gv_attr(_, _, _, _, _, _),
diff --git a/gv_color.pl b/gv_color.pl
index cf92f56..70e0495 100644
--- a/gv_color.pl
+++ b/gv_color.pl
@@ -124,7 +124,7 @@ gv_color_init:-
 % The persistent store is still fresh.
 gv_color_update(Age):-
   once(gv_color(_, _)),
-  Age < 3600, !.
+  Age < 8640000, !.
 % The persistent store has become stale, so refresh it.
 gv_color_update(_):-
   retractall_gv_color(_, _),

diff --git a/Prolog-Library-Collection b/Prolog-Library-Collection
index 03d4b46..af1a250 160000
--- a/Prolog-Library-Collection
+++ b/Prolog-Library-Collection
@@ -1 +1 @@
-Subproject commit 03d4b46ba9c6f658828ff843e5785c221ffc3a57
+Subproject commit af1a250d6074d0ab61a525fd064bfd555c5815a1
diff --git a/plHtml b/plHtml
index 50743da..81eb731 160000
--- a/plHtml
+++ b/plHtml
@@ -1 +1 @@
-Subproject commit 50743daad8dd0f3664e1cafbc14523a423314f84
+Subproject commit 81eb731eb46d98979c8f2862cfbf0e0aca9c1ef8

diff --git a/load.pl b/load.pl
index d502d58..4b117d1 100644
--- a/load.pl
+++ b/load.pl
@@ -1,11 +1,11 @@
 % Load file for plGraphViz.

-:- multifile(user:prolog/3).
 :- dynamic(user:prolog/3).
-user:project(plGraphViz, 'GraphViz support for SWI-Prolog.', plGraphViz).
+:- multifile(user:prolog/3).
+   user:project(plGraphViz, 'GraphViz support for SWI-Prolog.', plGraphViz).

 :- use_module(load_project).
-:- load_project([
+:- load_project(plGraphViz, [
     plc-'Prolog-Library-Collection',
     plHtml
 ]).
diff --git a/load_project.pl b/load_project.pl
index 3eae83d..5599b5e 100644
--- a/load_project.pl
+++ b/load_project.pl
@@ -1,7 +1,8 @@
 :- module(
   load_project,
   [
-    load_project/1, % +ChildProjects:list(or([atom,pair(atom)]))
+    load_project/2, % +Parent:atom
+                    % +ChildProjects:list(or([atom,pair(atom)]))
     load_subproject/2, % +ParentFileSearchPath:atom
                        % +Child:or([atom,pair(atom)])
     set_data_subdirectory/1 % +ParentDirectory:atom
@@ -16,19 +17,24 @@ Generic code for loading a project:
   * Load the index of subprojects onto the file search path.

 @author Wouter Beek
-@version 2014/05/27
+@version 2014/06/14
 */

-:- use_module(library(ansi_term)).
+:- use_module(library(ansi_term)). % Colorized terminal messages.
 :- use_module(library(apply)).

+:- dynamic(user:project/2).
+:- multifile(user:project/2).
+:- dynamic(user:project/3).
+:- multifile(user:project/3).


-load_project(ChildProjects):-
-  user:project(_, _, ParentFsp),
+
+load_project(Parent, ChildProjects):-
+  parent_alias(Parent, ParentFsp),

   % Entry point.
-  source_file(load_project(_), ThisFile),
+  source_file(load_project(_,_), ThisFile),
   file_directory_name(ThisFile, ThisDir),
   assert(user:file_search_path(ParentFsp, ThisDir)),
   assert(user:file_search_path(project, ThisDir)),
@@ -38,7 +44,7 @@ load_project(ChildProjects):-

   % Load the root of submodules onto the file search path.
   maplist(load_subproject(ParentFsp), ChildProjects),
-  
+
   % Load the index into the file search path.
   load_project_index(ParentFsp).

@@ -77,8 +83,20 @@ load_subproject_file_search_path(_, ChildFsp, ChildDir):-

 load_project_index(Fsp):-
   Spec =.. [Fsp,index],
-  absolute_file_name(Spec, File, [access(read),file_type(prolog)]),
+  absolute_file_name(
+    Spec,
+    File,
+    [access(read),file_errors(fail),file_type(prolog)]
+  ), !,
   ensure_loaded(File).
+load_project_index(_).
+
+
+%! parent_alias(+Parent:atom, -ParentFsp:atom) is det.
+
+parent_alias(Parent, ParentFsp):-
+  user:project(Parent, _, ParentFsp), !.
+parent_alias(Parent, Parent).


 %! set_data_subdirectory(+ParentDirectory:atom) is det.

diff --git a/Prolog-Library-Collection b/Prolog-Library-Collection
index af1a250..5b34b01 160000
--- a/Prolog-Library-Collection
+++ b/Prolog-Library-Collection
@@ -1 +1 @@
-Subproject commit af1a250d6074d0ab61a525fd064bfd555c5815a1
+Subproject commit 5b34b01ab0cc82a56e6fd90fc26e75da22f5a0fe
diff --git a/plHtml b/plHtml
index 81eb731..08480c4 160000
--- a/plHtml
+++ b/plHtml
@@ -1 +1 @@
-Subproject commit 81eb731eb46d98979c8f2862cfbf0e0aca9c1ef8
+Subproject commit 08480c40acaee5f70bfb21e3c641bef1e7d258bd

diff --git a/gv_attr_type.pl b/gv_attr_type.pl
index 200c034..f9a0e7f 100644
--- a/gv_attr_type.pl
+++ b/gv_attr_type.pl
@@ -29,18 +29,13 @@
     smoothType//1, % +SmoothType:atom
     %splineType//1,
     %startType//1,
+    string//1, % ?Content:atom
     style//2 % +Context:oneof([cluster,edge,node])
              % +Style:atom
     %viewPort//1
   ]
 ).
 :- reexport(
-  library(dcg/basics),
-  [
-    string//1 % +String:atom
-  ]
-).
-:- reexport(
   plGraphViz(gv_color),
   [
     color//1, % +Color:compound
@@ -383,6 +378,13 @@ smoothType(triangle).
 % @tbd startType


+%! string(?Content:atom)// .
+% A GraphViz string.
+
+string(Content) -->
+  atom(Content).
+
+
 %! style(?Context:oneof([cluster,edge,node]), ?Style:atom) is nondet.

 style(Context, Style) -->
diff --git a/gv_attrs.pl b/gv_attrs.pl
index fa499d0..dd0145a 100644
--- a/gv_attrs.pl
+++ b/gv_attrs.pl
@@ -68,7 +68,7 @@ gv_attr(Context, N=V1, N=V2):-
   ;
     Dcg =.. [Type,V1]
   ),
-  dcg_phrase(Dcg, V2),
+  once(dcg_phrase(Dcg, V2)),
   check_minimum(V1, Minimum).

 check_minimum(_, ''):- !.
diff --git a/gv_color.pl b/gv_color.pl
index 70e0495..19d6e05 100644
--- a/gv_color.pl
+++ b/gv_color.pl
@@ -23,6 +23,7 @@

 :- use_module(dcg(dcg_abnf)).
 :- use_module(dcg(dcg_cardinal)).
+:- use_module(dcg(dcg_content)).
 :- use_module(generics(db_ext)).
 :- use_module(os(file_ext)).
 :- use_module(sparql(sparql_char)).
@@ -46,14 +47,17 @@
 %   2. `rgba(Red:nonneg,Green:nonneg,Blue:nonneg,Alpha:nonneg)`
 %   3. `hsv(Hue:between(0.0,1.0),Saturation:between(0.0,1.0),Value:between(0.0,1.0))`

-color(rgb(Red,Green,Blue)) -->
+color(rgb(Red,Green,Blue)) --> !,
   `#`,
   '#'(3, hex_color, [Red,Green,Blue]).
-color(rgbs(Red,Green,Blue,Alpha)) -->
+color(rgbs(Red,Green,Blue,Alpha)) --> !,
   `#`,
   '#'(4, hex_color, [Red,Green,Blue,Alpha]).
-color(hsv(Hue,Saturation,Value)) -->
+color(hsv(Hue,Saturation,Value)) --> !,
   '#'(3, hsv_color, [Hue,Saturation,Value]).
+color(Name) -->
+  {gv_color(_, Name)},
+  atom(Name).

 hex_color(I) -->
   {W1 is I / 16},
diff --git a/gv_file.pl b/gv_file.pl
index 827f680..fe63e28 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -1,16 +1,13 @@
 :- module(
   gv_file,
   [
-    graph_to_gv_file/3, % +Options:list(nvpair)
+    gif_to_gv_file/3, % +Options:list(nvpair)
                         % +GraphInterchangeFormat:compound
                         % ?ToFile:atom
     graph_to_svg_dom/3, % +Options:list(nvpair)
                         % +GraphInterchangeFormat:compound
                         % -SvgDom:list(compound)
-    open_dot/1, % +File:file
-    tree_to_gv_file/3 % +Options:list(nvpair)
-                      % +Tree:compound
-                      % ?ToFile:atom
+    open_dot/1 % +File:file
   ]
 ).

@@ -81,7 +78,7 @@ user:prolog_file_type(xdot, xdot).



-%! graph_to_gv_file(
+%! gif_to_gv_file(
 %!   +Options:list(nvpair),
 %!   +GIF:compound,
 %!   -ToFile:atom
@@ -99,7 +96,7 @@ user:prolog_file_type(xdot, xdot).
 % @arg GIF A compound term representing a graph.
 % @arg ToFile The atomic name of a file.

-graph_to_gv_file(O1, GIF, ToFile):-
+gif_to_gv_file(O1, GIF, ToFile):-
   once(phrase(gv_graph(GIF), Codes)),
   to_gv_file(O1, Codes, ToFile).

@@ -117,7 +114,7 @@ graph_to_gv_file(O1, GIF, ToFile):-
 graph_to_svg_dom(O1, GIF, SvgDom):-
   % Make sure the file type of the output file is SvgDom.
   merge_options([to_file_type=svg], O1, O2),
-  graph_to_gv_file(O2, GIF, ToFile),
+  gif_to_gv_file(O2, GIF, ToFile),
   file_to_svg(ToFile, SvgDom),
   safe_delete_file(ToFile).

@@ -133,33 +130,6 @@ open_dot(File):-
   run_program(Program, [File]).


-%! tree_to_gv_file(+Options:list(nvpair), +Tree:compound, ?ToFile:atom) is det.
-% Stores the given tree term into a GraphViz file.
-%
-% The following options are supported:
-%   * =|method(+Method:oneof([dot,sfdp])|=
-%     The algorithm used by GraphViz for positioning the tree nodes.
-%     Either =dot= (default) or =sfdp=.
-%   * =|to_file_type(+FileType:oneof([jpeg,pdf,svg,xdot])|=
-%     The file type of the generated GraphViz file.
-%
-% @arg Options A list of name-value pairs.
-% @arg Tree A compound term representing a tree.
-% @arg ToFile The atomic name of the generated file.
-
-tree_to_gv_file(O1, Tree, ToFile):-
-  once(phrase(gv_tree(O1, Tree), Codes)),
-  to_gv_file(O1, Codes, ToFile).
-
-gv_tree(O1, T) -->
-  {
-    tree_to_ugraph(T, UG),
-    merge_options([edge_labels(false)], O1, O2),
-    export_ugraph(O2, UG, G_Term)
-  },
-  gv_graph(G_Term).
-
-

 % SUPPORT PREDICATES %

diff --git a/gv_gif.pl b/gv_gif.pl
new file mode 100644
index 0000000..becf7e2
--- /dev/null
+++ b/gv_gif.pl
@@ -0,0 +1,109 @@
+:- module(
+  gv_gif,
+  [
+    create_gif/3, % +Edges:ordset
+                  % -Gif:compound
+                  % +Options:list(nvpair)
+    create_gif/4 % +Vertices:ordset
+                 % +Edges:ordset
+                 % -Gif:compound
+                 % +Options:list(nvpair)
+  ]
+).
+
+/** <module> GraphViz Graph Interchange Format (GIF)
+
+Support for creating GIF representations.
+
+@author Wouter Beek
+@version 2014/06
+*/
+
+:- use_module(library(apply)).
+:- use_module(library(ordsets)).
+
+:- use_module(generics(list_ext)).
+
+:- use_module(plRdf(rdf_name)). % Meta-DCG.
+
+
+
+%! create_gif(+Edges:ordset, -Gif:compound, +Options:list(nvpair)) is det.
+
+create_gif(Es, Gif, Options):-
+  edges_to_vertices(Es, Vs),
+  create_gif(Vs, Es, Gif, Options).
+
+%! create_gif(
+%!   +Vertices:ordset,
+%!   +Edges:ordset,
+%!   -Gif:compound,
+%!   +Options:list(nvpair)
+%! ) is det.
+
+create_gif(Vs, Es, graph(V_Terms,E_Terms,G_Attrs), Options):-
+  maplist(vertex_term0(Vs, Options), Vs, V_Terms),
+  maplist(edge_term0(Vs, Options), Es, E_Terms),
+  G_Attrs = [directed=true].
+
+edge_term0(Vs, Options, E, E_Term):-
+  edge_term(Vs, E, E_Term, Options).
+
+vertex_term0(Vs, Options, V, V_Term):-
+  vertex_term(Vs, V, V_Term, Options).
+
+
+%! edge_term(
+%!   +Vertices:ordset,
+%!   +Edge:pair,
+%!   -EdgeTerm:compound,
+%!   +Options:list(nvpair)
+%! ) is det.
+
+edge_term(Vs, E, edge(FromId,ToId,E_Attrs), _):-
+  edge_components(E, FromV, _, ToV),
+  nth0chk(FromId, Vs, FromV),
+  nth0chk(ToId, Vs, ToV),
+  E_Attrs = [].
+
+
+%! vertex_term(
+%!   +Vertices:ordset,
+%!   +Vertex,
+%!   -VertexTerm:compound,
+%!   +Options:list(nvpair)
+%! ) is det.
+
+vertex_term(Vs, V, vertex(Id,V,V_Attrs), Options):-
+  nth0chk(Id, Vs, V),
+  
+  % Label.
+  option(vertex_label(VertexLabel), Options, =),
+  call(VertexLabel, V, V_Label),
+  
+  V_Attrs = [label=V_Label].
+
+vertex_label(V, V_Label):-
+  dcg_with_output_to(atom(V_Label), rdf_term_name([literal_ellipsis(50)], V)).
+
+
+
+% Helpers
+
+%! edge_components(+Edge:compound, -FromVertex, -EdgeType, -ToVertex) is det.
+%! edge_components(-Edge:compound, +FromVertex, ?EdgeType, +ToVertex) is det.
+
+edge_components(FromV-EdgeType-ToV, FromV, EdgeType, ToV):-
+  nonvar(EdgeType).
+edge_components(FromV-ToV, FromV, EdgeType, ToV):-
+  var(EdgeType).
+
+
+%! edges_to_vertices(+Edges:ordset, -Vertices:ordset) is det.
+
+edges_to_vertices([], []):- !.
+edges_to_vertices([S-_-O|T], S3):-
+  edges_to_vertices(T, S1),
+  ord_add_element(S1, S, S2),
+  ord_add_element(S2, O, S3).
+
diff --git a/gv_tree.pl b/gv_tree.pl
new file mode 100644
index 0000000..4412a90
--- /dev/null
+++ b/gv_tree.pl
@@ -0,0 +1,39 @@
+:- module(
+  gv_tree,
+  [
+    tree_to_gv_file/3 % +Options:list(nvpair)
+                      % +Tree:compound
+                      % ?ToFile:atom
+  ]
+).
+
+/** <module> GraphViz tree
+
+Export trees to GraphViz.
+
+@author Wouter Beek
+@version 2014/06
+*/
+
+:- use_module(library(aggregate)).
+
+:- use_module(generics(trees)).
+
+:- use_module(plGraphViz(gv_file)).
+:- use_module(plGraphViz(gv_gif)).
+
+
+%! tree_to_gv_file(+Options:list(nvpair), +Tree:compound, ?ToFile:atom) is det.
+% Stores the given tree term into a GraphViz file.
+%
+% Options are passed on to create_gif/3 and gif_to_gv_file/3.
+
+tree_to_gv_file(Options, Tree, ToFile):-
+  tree_to_gif(Tree, Gif, Options),
+  gif_to_gv_file(Options, Gif, ToFile).
+
+
+tree_to_gif(H-T, Gif, Options):-
+  tree_to_vertices_edges(Tree, Vs, Es),
+  create_gif(Vs, Es, Gif, Options).
+

diff --git a/gv_attr_type.pl b/gv_attr_type.pl
index f9a0e7f..7a64c82 100644
--- a/gv_attr_type.pl
+++ b/gv_attr_type.pl
@@ -191,7 +191,7 @@ doubleList1(Float) -->
   double(Float).


-%! escString(+String:atom)// ,
+%! escString(+String:atom)// .
 % @tbd Support for context-dependent replacements.

 escString(String) -->

diff --git a/gv_file.pl b/gv_file.pl
index fe63e28..c780692 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -1,12 +1,12 @@
 :- module(
   gv_file,
   [
-    gif_to_gv_file/3, % +Options:list(nvpair)
-                        % +GraphInterchangeFormat:compound
-                        % ?ToFile:atom
-    graph_to_svg_dom/3, % +Options:list(nvpair)
-                        % +GraphInterchangeFormat:compound
+    gif_to_gv_file/3, % +GraphInterchangeFormat:compound
+                      % ?ToFile:atom
+                      % +Options:list(nvpair)
+    graph_to_svg_dom/3, % +GraphInterchangeFormat:compound
                         % -SvgDom:list(compound)
+                        % +Options:list(nvpair)
     open_dot/1 % +File:file
   ]
 ).
@@ -20,11 +20,12 @@ Also converts between GraphViz DOT formatted files
 and GraphViz output files or SVG DOM structures.

 @author Wouter Beek
-@version 2011-2013/09, 2013/11-2014/01, 2014/05
+@version 2011-2013/09, 2013/11-2014/01, 2014/05, 2014/07
 */

 :- use_module(library(option)).
 :- use_module(library(process)).
+:- use_module(library(predicate_options)). % Declarations.

 :- use_module(generics(codes_ext)).
 :- use_module(generics(db_ext)).
@@ -48,73 +49,76 @@ and GraphViz output files or SVG DOM structures.
 :- multifile(user:prolog_file_type/2).

 % Register DOT.
-user:prolog_file_type(dot, dot).
-user:prolog_file_type(dot, graphviz).
-user:file_type_program(dot, dotty).
-user:file_type_program(dot, dotx).
-user:module_uses(gv_file, file_type(dot)).
+:- db_add_novel(user:prolog_file_type(dot, dot)).
+:- db_add_novel(user:prolog_file_type(dot, graphviz)).
+:- db_add_novel(user:file_type_program(dot, dotty)).
+:- db_add_novel(user:file_type_program(dot, dotx)).
+:- db_add_novel(user:module_uses(gv_file, file_type(dot))).

 % Register JPG/JPEG.
-user:prolog_file_type(jpeg, jpeg).
-user:prolog_file_type(jpeg, graphviz_output).
-user:prolog_file_type(jpg, jpeg).
-user:prolog_file_type(jpg, graphviz_output).
+:- db_add_novel(user:prolog_file_type(jpeg, jpeg)).
+:- db_add_novel(user:prolog_file_type(jpeg, graphviz_output)).
+:- db_add_novel(user:prolog_file_type(jpg, jpeg)).
+:- db_add_novel(user:prolog_file_type(jpg, graphviz_output)).

 % Register PDF.
-user:prolog_file_type(pdf, pdf).
-user:prolog_file_type(pdf, graphviz_output).
+:- db_add_novel(user:prolog_file_type(pdf, pdf)).
+:- db_add_novel(user:prolog_file_type(pdf, graphviz_output)).

 % Register PNG.
-user:prolog_file_type(png, png).
-user:prolog_file_type(png, graphviz_output).
+:- db_add_novel(user:prolog_file_type(png, png)).
+:- db_add_novel(user:prolog_file_type(png, graphviz_output)).

 % Register SVG.
-user:prolog_file_type(svg, graphviz_output).
-user:prolog_file_type(svg, svg).
+:- db_add_novel(user:prolog_file_type(svg, graphviz_output)).
+:- db_add_novel(user:prolog_file_type(svg, svg)).

 % Register XDOT.
-user:prolog_file_type(xdot, graphviz_output).
-user:prolog_file_type(xdot, xdot).
-
-
-
-%! gif_to_gv_file(
-%!   +Options:list(nvpair),
-%!   +GIF:compound,
-%!   -ToFile:atom
-%! ) is det.
+:- db_add_novel(user:prolog_file_type(xdot, graphviz_output)).
+:- db_add_novel(user:prolog_file_type(xdot, xdot)).
+
+:- predicate_options(graph_to_svg_dom/3, 3, [
+     pass_to(gif_to_gv_file/3, 3)
+   ]).
+:- predicate_options(gif_to_gv_file/3, 3, [
+     pass_to(to_gv_file/3, 3)
+   ]).
+:- predicate_options(to_gv_file/3, 3, [
+     pass_to(convert_gv/3, 3)
+   ]).
+:- predicate_options(convert_gv/3, 3, [
+     method(+oneof([dot,sfdp])),
+     to_file_type(+oneof([dot,jpeg,pdf,svg,xdot]))
+   ]).
+
+
+
+%! gif_to_gv_file(+Gif:compound, -ToFile:atom, +Options:list(nvpair)) is det.
 % Returns a file containing a GraphViz visualization of the given graph.
 %
 % The following options are supported:
 %   * =|method(+Method:oneof([dot,sfdp])|=
 %     The algorithm used by GraphViz for positioning the tree nodes.
 %     Either =dot= (default) or =sfdp=.
-%   * =|to_file_type(+FileType:oneof([jpeg,pdf,svg,xdot])|=
+%   * =|to_file_type(+FileType:oneof([dot,jpeg,pdf,svg,xdot])|=
 %     The file type of the generated GraphViz file.
-%
-% @arg Options A list of name-value pairs.
-% @arg GIF A compound term representing a graph.
-% @arg ToFile The atomic name of a file.
+%     Default: `pdf`.

-gif_to_gv_file(O1, GIF, ToFile):-
-  once(phrase(gv_graph(GIF), Codes)),
-  to_gv_file(O1, Codes, ToFile).
+gif_to_gv_file(Gif, ToFile, Options):-
+  once(phrase(gv_graph(Gif), Codes)),
+  to_gv_file(Codes, ToFile, Options).


 %! graph_to_svg_dom(
-%!   +Options:list(nvpair),
 %!   +GraphInterchangeFormat:compound,
-%!   -SvgDom:list(compound)
+%!   -SvgDom:list(compound),
+%!   +Options:list(nvpair)
 %! ) is det.
-% The following options are supported:
-%   * =|method(+Method:oneof([dot,sfdp])|=
-%     The algorithm used by GraphViz for positioning the tree nodes.
-%     Either =dot= (default) or =sfdp=.

-graph_to_svg_dom(O1, GIF, SvgDom):-
+graph_to_svg_dom(Gif, SvgDom, Options1):-
   % Make sure the file type of the output file is SvgDom.
-  merge_options([to_file_type=svg], O1, O2),
-  gif_to_gv_file(O2, GIF, ToFile),
+  merge_options([to_file_type=svg], Options1, Options2),
+  gif_to_gv_file(Gif, ToFile, Options2),
   file_to_svg(ToFile, SvgDom),
   safe_delete_file(ToFile).

@@ -133,31 +137,23 @@ open_dot(File):-

 % SUPPORT PREDICATES %

-%! convert_gv(+Options:list(nvpair), +FromFile:atom, ?ToFile:atom) is det.
+%! convert_gv(+FromFile:atom, ?ToFile:atom, +Options:list(nvpair)) is det.
 % Converts a GraphViz DOT file to an image file, using a specific
 % visualization method.
-%
-% The following options are supported:
-%   * =|method(+Method:oneof([dot,sfdp])|=
-%     The algorithm used by GraphViz for positioning the tree nodes.
-%     Either =dot= (default) or =sfdp=.
-%   * =|to_file_type(+FileType:oneof([jpeg,pdf,svg,xdot])|=
-%     The file type of the generated GraphViz file.
-%
-% @arg Options
-% @arg FromFile
-% @arg ToFile

-convert_gv(O1, FromFile, ToFile):-
+convert_gv(FromFile, ToFile, Options):-
+  option(to_file_type(dot), Options), !,
+  rename_file(FromFile, ToFile).
+convert_gv(FromFile, ToFile, Options):-
   % The input file must be readable.
   access_file(FromFile, read),

   % The method option.
-  option(method(Method), O1, dot),
+  option(method(Method), Options, dot),
   must_be(oneof([dot,sfdp]), Method),

   % The file type option.
-  option(to_file_type(ToFileType), O1, pdf),
+  option(to_file_type(ToFileType), Options, pdf),
   prolog_file_type(ToExtension, ToFileType),
   prolog_file_type(ToExtension, graphviz_output), !,

@@ -189,15 +185,10 @@ convert_gv(O1, FromFile, ToFile):-
   process_wait(PID, exit(ShellStatus)),
   exit_code_handler('GraphViz', ShellStatus).

-%! to_gv_file(+Options:list(nvpair), +Codes:list(code), ?ToFile:atom) is det.
-% The following options are supported:
-%   * =|method(+Method:oneof([dot,sfdp])|=
-%     The algorithm used by GraphViz for positioning the tree nodes.
-%     Either =dot= (default) or =sfdp=.
-%   * =|to_file_type(+FileType:oneof([jpeg,pdf,svg,xdot])|=
-%     The file type of the generated GraphViz file.

-to_gv_file(O1, Codes, ToFile):-
+%! to_gv_file(+Codes:list(code), ?ToFile:atom, +Options:list(nvpair)) is det.
+
+to_gv_file(Codes, ToFile, Options):-
   absolute_file_name(
     data(tmp),
     FromFile,
@@ -208,13 +199,13 @@ to_gv_file(O1, Codes, ToFile):-
     put_codes(Out, Codes),
     close(Out)
   ),
-  convert_gv(O1, FromFile, ToFile),
+  convert_gv(FromFile, ToFile, Options),

-  % DEB: Store DOT file.
-  ignore((
-    file_type_alternative(ToFile, graphviz, DOT_File),
-    safe_copy_file(FromFile, DOT_File)
-  )),
+  %%%%% DEB: Store DOT file.
+  %%%%ignore((
+  %%%%  file_type_alternative(ToFile, graphviz, DOT_File),
+  %%%%  safe_copy_file(FromFile, DOT_File)
+  %%%%)),

   safe_delete_file(FromFile).

diff --git a/gv_tree.pl b/gv_tree.pl
index 4412a90..afeb8f6 100644
--- a/gv_tree.pl
+++ b/gv_tree.pl
@@ -1,9 +1,9 @@
 :- module(
   gv_tree,
   [
-    tree_to_gv_file/3 % +Options:list(nvpair)
-                      % +Tree:compound
+    tree_to_gv_file/3 % +Tree:compound
                       % ?ToFile:atom
+                      % +Options:list(nvpair)
   ]
 ).

@@ -12,7 +12,7 @@
 Export trees to GraphViz.

 @author Wouter Beek
-@version 2014/06
+@version 2014/06-2014/07
 */

 :- use_module(library(aggregate)).
@@ -23,14 +23,18 @@ Export trees to GraphViz.
 :- use_module(plGraphViz(gv_gif)).


-%! tree_to_gv_file(+Options:list(nvpair), +Tree:compound, ?ToFile:atom) is det.
+%! tree_to_gv_file(
+%!   +Tree:compound,
+%!   ?ToFile:atom,
+%!   +Options:list(nvpair)
+%! ) is det.
 % Stores the given tree term into a GraphViz file.
 %
 % Options are passed on to create_gif/3 and gif_to_gv_file/3.

-tree_to_gv_file(Options, Tree, ToFile):-
+tree_to_gv_file(Tree, ToFile, Options):-
   tree_to_gif(Tree, Gif, Options),
-  gif_to_gv_file(Options, Gif, ToFile).
+  gif_to_gv_file(Gif, ToFile, Options).


 tree_to_gif(H-T, Gif, Options):-

diff --git a/gv_file.pl b/gv_file.pl
index c780692..9cb1f95 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -4,9 +4,9 @@
     gif_to_gv_file/3, % +GraphInterchangeFormat:compound
                       % ?ToFile:atom
                       % +Options:list(nvpair)
-    graph_to_svg_dom/3, % +GraphInterchangeFormat:compound
-                        % -SvgDom:list(compound)
-                        % +Options:list(nvpair)
+    gif_to_svg_dom/3, % +GraphInterchangeFormat:compound
+                      % -SvgDom:list(compound)
+                      % +Options:list(nvpair)
     open_dot/1 % +File:file
   ]
 ).
@@ -77,7 +77,7 @@ and GraphViz output files or SVG DOM structures.
 :- db_add_novel(user:prolog_file_type(xdot, graphviz_output)).
 :- db_add_novel(user:prolog_file_type(xdot, xdot)).

-:- predicate_options(graph_to_svg_dom/3, 3, [
+:- predicate_options(gif_to_svg_dom/3, 3, [
      pass_to(gif_to_gv_file/3, 3)
    ]).
 :- predicate_options(gif_to_gv_file/3, 3, [
@@ -109,13 +109,13 @@ gif_to_gv_file(Gif, ToFile, Options):-
   to_gv_file(Codes, ToFile, Options).


-%! graph_to_svg_dom(
+%! gif_to_svg_dom(
 %!   +GraphInterchangeFormat:compound,
 %!   -SvgDom:list(compound),
 %!   +Options:list(nvpair)
 %! ) is det.

-graph_to_svg_dom(Gif, SvgDom, Options1):-
+gif_to_svg_dom(Gif, SvgDom, Options1):-
   % Make sure the file type of the output file is SvgDom.
   merge_options([to_file_type=svg], Options1, Options2),
   gif_to_gv_file(Gif, ToFile, Options2),

diff --git a/gv_file.pl b/gv_file.pl
index 9cb1f95..98cb0a2 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -1,8 +1,13 @@
 :- module(
   gv_file,
   [
+    file_to_gv/2, % +File:atom
+                  % +Options:list(nvpair)
+    file_to_gv/3, % +FromFile:atom
+                  % ?ToFile:atom
+                  % +Options:list(nvpair)
     gif_to_gv_file/3, % +GraphInterchangeFormat:compound
-                      % ?ToFile:atom
+                      % +ToFile:atom
                       % +Options:list(nvpair)
     gif_to_svg_dom/3, % +GraphInterchangeFormat:compound
                       % -SvgDom:list(compound)
@@ -23,6 +28,7 @@ and GraphViz output files or SVG DOM structures.
 @version 2011-2013/09, 2013/11-2014/01, 2014/05, 2014/07
 */

+:- use_module(library(memfile)).
 :- use_module(library(option)).
 :- use_module(library(process)).
 :- use_module(library(predicate_options)). % Declarations.
@@ -77,74 +83,60 @@ and GraphViz output files or SVG DOM structures.
 :- db_add_novel(user:prolog_file_type(xdot, graphviz_output)).
 :- db_add_novel(user:prolog_file_type(xdot, xdot)).

-:- predicate_options(gif_to_svg_dom/3, 3, [
-     pass_to(gif_to_gv_file/3, 3)
-   ]).
-:- predicate_options(gif_to_gv_file/3, 3, [
-     pass_to(to_gv_file/3, 3)
+:- predicate_options(codes_to_gv_file/3, 3, [
+     pass_to(file_to_gv/3, 3)
    ]).
-:- predicate_options(to_gv_file/3, 3, [
-     pass_to(convert_gv/3, 3)
+:- predicate_options(file_to_gv/2, 2, [
+     pass_to(file_to_gv/3, 3)
    ]).
-:- predicate_options(convert_gv/3, 3, [
+:- predicate_options(file_to_gv/3, 3, [
      method(+oneof([dot,sfdp])),
      to_file_type(+oneof([dot,jpeg,pdf,svg,xdot]))
    ]).
+:- predicate_options(gif_to_svg_dom/3, 3, [
+     pass_to(gif_to_gv_file/3, 3)
+   ]).
+:- predicate_options(gif_to_gv_file/3, 3, [
+     pass_to(codes_to_gv_file/3, 3)
+   ]).



-%! gif_to_gv_file(+Gif:compound, -ToFile:atom, +Options:list(nvpair)) is det.
-% Returns a file containing a GraphViz visualization of the given graph.
-%
-% The following options are supported:
-%   * =|method(+Method:oneof([dot,sfdp])|=
-%     The algorithm used by GraphViz for positioning the tree nodes.
-%     Either =dot= (default) or =sfdp=.
-%   * =|to_file_type(+FileType:oneof([dot,jpeg,pdf,svg,xdot])|=
-%     The file type of the generated GraphViz file.
-%     Default: `pdf`.
-
-gif_to_gv_file(Gif, ToFile, Options):-
-  once(phrase(gv_graph(Gif), Codes)),
-  to_gv_file(Codes, ToFile, Options).
-
-
-%! gif_to_svg_dom(
-%!   +GraphInterchangeFormat:compound,
-%!   -SvgDom:list(compound),
+%! codes_to_gv_file(
+%!   +Codes:list(code),
+%!   +ToFile:atom,
 %!   +Options:list(nvpair)
 %! ) is det.

-gif_to_svg_dom(Gif, SvgDom, Options1):-
-  % Make sure the file type of the output file is SvgDom.
-  merge_options([to_file_type=svg], Options1, Options2),
-  gif_to_gv_file(Gif, ToFile, Options2),
-  file_to_svg(ToFile, SvgDom),
-  safe_delete_file(ToFile).
-
-
-%! open_dot(+File:atom) is det.
-% Opens the given DOT file.
-%
-% @tbd Test support on Windows.
-% @tbd Test support on OS-X.
-
-open_dot(File):-
-  once(find_program_by_file_type(dot, Program)),
-  run_program(Program, [File]).
+codes_to_gv_file(Codes, ToFile, Options):-
+  access_file(ToFile, write),
+  setup_call_cleanup(
+    new_memory_file(MemFile),
+    (
+      setup_call_cleanup(
+        open(MemFile, write, Write, [encoding(utf8),type(test)]),
+        put_codes(Write, Codes),
+        close(Write)
+      ),
+      file_to_gv(MemFile, ToFile, Options)
+    ),
+    free_memory_file(MemFile)
+  ).


+%! file_to_gv(+FromFile:atom, +Options:list(nvpair)) is det.

-% SUPPORT PREDICATES %
+file_to_gv(FromFile, Options):-
+  file_to_gv(FromFile, _, Options).

-%! convert_gv(+FromFile:atom, ?ToFile:atom, +Options:list(nvpair)) is det.
+%! file_to_gv(+FromFile:atom, ?ToFile:atom, +Options:list(nvpair)) is det.
 % Converts a GraphViz DOT file to an image file, using a specific
 % visualization method.

-convert_gv(FromFile, ToFile, Options):-
+file_to_gv(FromFile, ToFile, Options):-
   option(to_file_type(dot), Options), !,
   rename_file(FromFile, ToFile).
-convert_gv(FromFile, ToFile, Options):-
+file_to_gv(FromFile, ToFile, Options):-
   % The input file must be readable.
   access_file(FromFile, read),

@@ -186,26 +178,43 @@ convert_gv(FromFile, ToFile, Options):-
   exit_code_handler('GraphViz', ShellStatus).


-%! to_gv_file(+Codes:list(code), ?ToFile:atom, +Options:list(nvpair)) is det.
+%! gif_to_gv_file(+Gif:compound, +ToFile:atom, +Options:list(nvpair)) is det.
+% Returns a file containing a GraphViz visualization of the given graph.
+%
+% The following options are supported:
+%   * =|method(+Method:oneof([dot,sfdp])|=
+%     The algorithm used by GraphViz for positioning the tree nodes.
+%     Either =dot= (default) or =sfdp=.
+%   * =|to_file_type(+FileType:oneof([dot,jpeg,pdf,svg,xdot])|=
+%     The file type of the generated GraphViz file.
+%     Default: `pdf`.
+
+gif_to_gv_file(Gif, ToFile, Options):-
+  once(phrase(gv_graph(Gif), Codes)),
+  codes_to_gv_file(Codes, ToFile, Options).
+
+
+%! gif_to_svg_dom(
+%!   +GraphInterchangeFormat:compound,
+%!   -SvgDom:list(compound),
+%!   +Options:list(nvpair)
+%! ) is det.
+
+gif_to_svg_dom(Gif, SvgDom, Options1):-
+  % Make sure the file type of the output file is SvgDom.
+  merge_options([to_file_type=svg], Options1, Options2),
+  gif_to_gv_file(Gif, ToFile, Options2),
+  file_to_svg(ToFile, SvgDom),
+  safe_delete_file(ToFile).

-to_gv_file(Codes, ToFile, Options):-
-  absolute_file_name(
-    data(tmp),
-    FromFile,
-    [access(write),file_type(graphviz)]
-  ),
-  setup_call_cleanup(
-    open(FromFile, write, Out, [encoding(utf8),type(test)]),
-    put_codes(Out, Codes),
-    close(Out)
-  ),
-  convert_gv(FromFile, ToFile, Options),

-  %%%%% DEB: Store DOT file.
-  %%%%ignore((
-  %%%%  file_type_alternative(ToFile, graphviz, DOT_File),
-  %%%%  safe_copy_file(FromFile, DOT_File)
-  %%%%)),
+%! open_dot(+File:atom) is det.
+% Opens the given DOT file.
+%
+% @tbd Test support on Windows.
+% @tbd Test support on OS-X.

-  safe_delete_file(FromFile).
+open_dot(File):-
+  once(find_program_by_file_type(dot, Program)),
+  run_program(Program, [File]).

diff --git a/gv_gif.pl b/gv_gif.pl
index becf7e2..908b9bc 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -16,16 +16,35 @@
 Support for creating GIF representations.

 @author Wouter Beek
-@version 2014/06
+@version 2014/06-2014/07
 */

 :- use_module(library(apply)).
+:- use_module(library(lambda)).
+:- use_module(library(option)).
 :- use_module(library(ordsets)).
+:- use_module(library(predicate_options)). % Declarations.

 :- use_module(generics(list_ext)).
+:- use_module(generics(option_ext)).
+:- use_module(graph_theory(graph_generic)).

 :- use_module(plRdf(rdf_name)). % Meta-DCG.

+:- predicate_options(create_gif/3, 3, [
+     pass_to(create_gif/4, 4)
+   ]).
+:- predicate_options(create_gif/4, 4, [
+     pass_to(vertex_term/3, 3),
+     pass_to(edge_term/3, 3),
+     graph_label(+atom)
+   ]).
+:- predicate_options(edge_term/3, 3, [
+   ]).
+:- predicate_options(vertex_term/3, 3, [
+     vertex_label(+atom)
+   ]).
+


 %! create_gif(+Edges:ordset, -Gif:compound, +Options:list(nvpair)) is det.
@@ -40,17 +59,28 @@ create_gif(Es, Gif, Options):-
 %!   -Gif:compound,
 %!   +Options:list(nvpair)
 %! ) is det.
-
-create_gif(Vs, Es, graph(V_Terms,E_Terms,G_Attrs), Options):-
-  maplist(vertex_term0(Vs, Options), Vs, V_Terms),
-  maplist(edge_term0(Vs, Options), Es, E_Terms),
-  G_Attrs = [directed=true].
-
-edge_term0(Vs, Options, E, E_Term):-
-  edge_term(Vs, E, E_Term, Options).
-
-vertex_term0(Vs, Options, V, V_Term):-
-  vertex_term(Vs, V, V_Term, Options).
+% The following options are supported:
+%   * =|graph_label(+LabelFunction)|=
+%     The functions that assigns names to graphs.
+%     No default.
+
+create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
+  % Vertex terms.
+  maplist(\V^VTerm^vertex_term(Vs, V, VTerm, Options), Vs, VTerms),
+  
+  % Edge terms.
+  maplist(\E^ETerm^edge_term(Vs, E, ETerm, Options), Es, ETerms),
+  
+  % Graph attributes.
+  (
+    option(graph_label(LabelFunction), Options)
+  ->
+    call(LabelFunction, Graph, GraphLabel)
+  ;
+    true
+  ),
+  
+  merge_options([directed=true,label=GraphLabel], GAttrs).


 %! edge_term(
@@ -60,11 +90,13 @@ vertex_term0(Vs, Options, V, V_Term):-
 %!   +Options:list(nvpair)
 %! ) is det.

-edge_term(Vs, E, edge(FromId,ToId,E_Attrs), _):-
-  edge_components(E, FromV, _, ToV),
+edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
+  edge_components(E, FromV, ToV),
+  
   nth0chk(FromId, Vs, FromV),
   nth0chk(ToId, Vs, ToV),
-  E_Attrs = [].
+  
+  EAttrs = [].


 %! vertex_term(
@@ -73,37 +105,16 @@ edge_term(Vs, E, edge(FromId,ToId,E_Attrs), _):-
 %!   -VertexTerm:compound,
 %!   +Options:list(nvpair)
 %! ) is det.
+% The following options are supported:
+%   * =|vertex_label(+LabelFunction)|=
+%     A function that assigns labels to vertices.

-vertex_term(Vs, V, vertex(Id,V,V_Attrs), Options):-
+vertex_term(Vs, V, vertex(Id,V,VAttrs), Options):-
   nth0chk(Id, Vs, V),

   % Label.
-  option(vertex_label(VertexLabel), Options, =),
-  call(VertexLabel, V, V_Label),
+  option(vertex_label(LabelFunction), Options, =),
+  call(LabelFunction, V, VLabel),

-  V_Attrs = [label=V_Label].
-
-vertex_label(V, V_Label):-
-  dcg_with_output_to(atom(V_Label), rdf_term_name([literal_ellipsis(50)], V)).
-
-
-
-% Helpers
-
-%! edge_components(+Edge:compound, -FromVertex, -EdgeType, -ToVertex) is det.
-%! edge_components(-Edge:compound, +FromVertex, ?EdgeType, +ToVertex) is det.
-
-edge_components(FromV-EdgeType-ToV, FromV, EdgeType, ToV):-
-  nonvar(EdgeType).
-edge_components(FromV-ToV, FromV, EdgeType, ToV):-
-  var(EdgeType).
-
-
-%! edges_to_vertices(+Edges:ordset, -Vertices:ordset) is det.
-
-edges_to_vertices([], []):- !.
-edges_to_vertices([S-_-O|T], S3):-
-  edges_to_vertices(T, S1),
-  ord_add_element(S1, S, S2),
-  ord_add_element(S2, O, S3).
+  VAttrs = [label=VLabel].

diff --git a/gv_dot.pl b/gv_dot.pl
index 9888973..68443ba 100644
--- a/gv_dot.pl
+++ b/gv_dot.pl
@@ -76,13 +76,13 @@ gv_compass_pt(sw) --> `sw`.
 gv_compass_pt(w) --> `w`.


-%! gv_edge_operator(+Directed:boolean)// .
+%! gv_edge_operator(+Directedness:boolean)// .
 % The binary edge operator between two vertices.
 % The operator that is used depends on whether the graph is directed or
 % undirected.
 %
-% @arg Directed Whether an edge is directed (operator `->`) or
-%               undirected (operator `--`).
+% @arg Directedness Whether an edge is directed (operator `->`) or
+%                   undirected (operator `--`).

 gv_edge_operator(false) --> !, `--`.
 gv_edge_operator(true) --> arrow(right, 2).
@@ -90,14 +90,14 @@ gv_edge_operator(true) --> arrow(right, 2).

 %! gv_edge_statement(
 %!   +Indent:nonneg,
-%!   +Directed:boolean,
+%!   +Directedness:boolean,
 %!   +GraphAttributes:list(nvpair),
 %!   +EdgeTerm:compound
 %! )// is det.
 % A GraphViz statement describing an edge.
 %
 % @arg Indent The indentation level at which the edge statement is written.
-% @arg Directed Whether the graph is directed or not.
+% @arg Directedness Whether the graph is directed or not.
 % @arg GraphAttributes The attributes of the graph. Some of these attributes
 %      may be used in the edge statement (e.g., the colorscheme).
 % @arg EdgeTerm A compound term in the GIFormat, representing an edge.
@@ -106,11 +106,11 @@ gv_edge_operator(true) --> arrow(right, 2).
 %      at the from and/or to location.
 % @tbd Add support for multiple, consecutive occurrences of gv_edge_rhs//2.

-gv_edge_statement(I, Directed, GAttrs, edge(FromId,ToId,EAttrs)) -->
+gv_edge_statement(I, Directedness, GAttrs, edge(FromId,ToId,EAttrs)) -->
   indent(I),
   gv_node_id(FromId), ` `,

-  gv_edge_operator(Directed), ` `,
+  gv_edge_operator(Directedness), ` `,

   gv_node_id(ToId), ` `,

@@ -148,11 +148,11 @@ gv_generic_attributes_statement(Kind, I, GraphAttrs, KindAttrs) -->
 %! gv_graph(+GraphTerm:compound)//
 % The follow graph attributes are supported,
 % beyond the GraphViz attributes for graphs:
-%   1. `directonality(+Directed:oneof([directed,undirected]))`
-%      A directed graph uses the keyword `digraph`.
-%      An undirected graph uses the keyword `graph`.
-%   2. `name(+GraphName:atom)`
-%   3. `strict(+StrictGraph:boolean)`
+%   * `directedness(+boolean)`
+%      Whether the graph is directed (`true`) or undirected (`false`).
+%      Default: `false`.
+%   * `name(+GraphName:atom)`
+%   * `strict(+StrictGraph:boolean)`
 %      This forbids the creation of self-arcs and multi-edges;
 %      they are ignored in the input file.
 %      Only in combinattion with directionality `directed`.
@@ -185,7 +185,7 @@ gv_graph(graph(VTerms, RankedVTerms, ETerms, GAttrs1)) -->
     shared_attributes(VTerms, SharedVAttrs, NewVTerms),
     shared_attributes(ETerms, SharedEAttrs, NewETerms),
     select_nvpair(strict=Strict, GAttrs1, GAttrs2, false),
-    select_nvpair(directed=Directed, GAttrs2, GAttrs3, true),
+    select_nvpair(directedness=Directedness, GAttrs2, GAttrs3, true),
     select_nvpair(name=GName, GAttrs3, GAttrs4, noname),
     add_default_nvpair(GAttrs4, overlap, false, GAttrs5),
     I = 0
@@ -195,24 +195,24 @@ gv_graph(graph(VTerms, RankedVTerms, ETerms, GAttrs1)) -->
   % States that this file represents a graph according to the GraphViz format.
   indent(I),
   gv_strict(Strict),
-  gv_graph_type(Directed), ` `,
+  gv_graph_type(Directedness), ` `,
   gv_id(GName), ` `,
   bracketed(
     curly,
-    gv_graph1(
+    gv_graph0(
       I,
       NewVTerms, SharedVAttrs, RankedVTerms,
       NewETerms, SharedEAttrs,
-      Directed, GAttrs5
+      Directedness, GAttrs5
     )
-  ),
+  ),                                                      
   newline.

-gv_graph1(
+gv_graph0(
   I,
   NewVTerms, SharedVAttrs, RankedVTerms,
   NewETerms, SharedEAttrs,
-  Directed, GAttrs
+  Directedness, GAttrs
 ) -->
   newline,

@@ -254,10 +254,10 @@ gv_graph1(
   },

   % The rank edges.
-  '*'(gv_edge_statement(NewI, Directed, GAttrs), RankEdges),
+  '*'(gv_edge_statement(NewI, Directedness, GAttrs), RankEdges),

   % The non-rank edges.
-  '*'(gv_edge_statement(NewI, Directed, GAttrs), NewETerms),
+  '*'(gv_edge_statement(NewI, Directedness, GAttrs), NewETerms),

   % Note that we do not include a newline here.

@@ -265,7 +265,7 @@ gv_graph1(
   indent(I).


-%! gv_graph_type(+Directed:boolean)// .
+%! gv_graph_type(+Directedness:boolean)// .
 % The type of graph that is represented.

 gv_graph_type(false) --> `graph`.
diff --git a/gv_gif.pl b/gv_gif.pl
index 908b9bc..4a3e75f 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -35,14 +35,25 @@ Support for creating GIF representations.
      pass_to(create_gif/4, 4)
    ]).
 :- predicate_options(create_gif/4, 4, [
-     pass_to(vertex_term/3, 3),
      pass_to(edge_term/3, 3),
-     graph_label(+atom)
+     pass_to(graph_attributes/2, 2),
+     pass_to(vertex_term/3, 3)
    ]).
 :- predicate_options(edge_term/3, 3, [
    ]).
+:- predicate_options(graph_attributes/2, 2, [
+     directedness(+boolean),
+     graph_colorscheme(+oneof([none,svg,x11]),
+     graph_label(+atom)
+   ]).
+
 :- predicate_options(vertex_term/3, 3, [
-     vertex_label(+atom)
+     vertex_color(+atom),
+     vertex_coordinates(+atom),
+     vertex_image(+atom),
+     vertex_label(+atom),
+     vertex_peripheries(+atom),
+     vertex_shape(+atom)
    ]).


@@ -60,6 +71,8 @@ create_gif(Es, Gif, Options):-
 %!   +Options:list(nvpair)
 %! ) is det.
 % The following options are supported:
+%   * =|graph_colorscheme(+oneof([none,svg,x11]))
+%     No default.
 %   * =|graph_label(+LabelFunction)|=
 %     The functions that assigns names to graphs.
 %     No default.
@@ -72,15 +85,7 @@ create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
   maplist(\E^ETerm^edge_term(Vs, E, ETerm, Options), Es, ETerms),

   % Graph attributes.
-  (
-    option(graph_label(LabelFunction), Options)
-  ->
-    call(LabelFunction, Graph, GraphLabel)
-  ;
-    true
-  ),
-  
-  merge_options([directed=true,label=GraphLabel], GAttrs).
+  graph_attributes(GAttrs, Options).


 %! edge_term(
@@ -89,14 +94,69 @@ create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
 %!   -EdgeTerm:compound,
 %!   +Options:list(nvpair)
 %! ) is det.
+% The following options are supported:
+%   * =|edge_arrowhead(+atom)|=
+%   * =|edge_color(+atom)|=
+%   * =|edge_label(+atom)|=
+%   * =|edge_style(+atom)|=

 edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
   edge_components(E, FromV, ToV),
-  
   nth0chk(FromId, Vs, FromV),
   nth0chk(ToId, Vs, ToV),

-  EAttrs = [].
+  % Arrowhead
+  if_option(edge_arrowhead(ArrowheadFunction), Options,
+    call(ArrowheadFunction, E, EArrowhead)
+  ),
+  
+  % Color.
+  if_option(edge_color(ColorFunction), Options,
+    call(ColorFunction, E, EColor)
+  ),
+  
+  % Label.
+  if_option(edge_label(LabelFunction), Options,
+    call(LabelFunction, E, ELabel)
+  ),
+  
+  % Style.
+  if_option(edge_style(StyleFunction), Options,
+    call(StyleFunction, E, EStyle)
+  ),
+  
+  EAttrs = [arrowHead=EArrowhead,color=EColor,label=ELabel,style=EStyle].
+
+
+%! graph_attributes(
+%!   -GraphAttributes:list(nvpair),
+%!   +Options:list(nvpair)
+%! ) is det.
+% The following options are supported:
+%   * =|directedness(+boolean)|=
+%     Whether the graph is directed (`true`) or undirected (`false`).
+%     Default: `false`.
+%   * =|graph_colorscheme(+oneof([none,svg,x11]))|=
+%     The colorscheme from which the color in this graph are taken.
+%     Default: `svg`.
+%   * =|graph_label(+atom)|=
+%     The graph label.
+%     No default.
+
+graph_attributes(GAttrs, Options):-
+  % Directedness.
+  option(directedness(Directedness), Options, false),
+  
+  % Colorscheme.
+  if_option(graph_colorscheme(Colorscheme), Options, true),
+  
+  % Label.
+  if_option(graph_label(GLabel), Options, true),
+  
+  merge_options(
+    [colorscheme=Colorscheme,directedness=Directedness,label=GLabel],
+    GAttrs
+  ).


 %! vertex_term(
@@ -106,15 +166,66 @@ edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
 %!   +Options:list(nvpair)
 %! ) is det.
 % The following options are supported:
+%   * =|vertex_color(+ColorFunction)|=
+%     A function that assigns colors to vertices.
+%     No default.
+%   * =|vertex_coordinate(+CoordinateFunction)|=
+%     A function that assigns coordinates to vertices.
+%     No default.
+%   * =|vertex_image(+ImageFunction)|=
+%     A function that assinges images to vertices.
+%     No default.
 %   * =|vertex_label(+LabelFunction)|=
 %     A function that assigns labels to vertices.
+%     No default.
+%   * =|vertex_peripheries(+PeripheriesFunction)|=
+%     A function that assinges peripheries to vertices.
+%     No default.
+%   * =|vertex_shape(+ShapeFunction)|=
+%     A function that assinges shapes to vertices.
+%     No default.

 vertex_term(Vs, V, vertex(Id,V,VAttrs), Options):-
   nth0chk(Id, Vs, V),

+  % Color.
+  if_option(vertex_color(ColorFunction), Options,
+    call(ColorFunction, V, VColor)
+  ),
+  
+  % Coordinates.
+  %%%%if_option(vertex_coordinate(CoordinateFunction), Options,
+  %%%%  call(CoordinateFunction, V, VCoordinates)
+  %%%%),
+  
+  % Image.
+  if_option(image(ImageFunction), Options,
+    call(ImageFunction, V, VImage)
+  ),
+  
   % Label.
-  option(vertex_label(LabelFunction), Options, =),
-  call(LabelFunction, V, VLabel),
+  if_option(vertex_label(LabelFunction), Options,
+    call(LabelFunction, V, VLabel)
+  ),
+  
+  % Peripheries.
+  if_option(vertex_peripheries(PeripheriesFunction), Options,
+    call(PeripheriesFunction, V, VPeripheries)
+  ),
+  
+  % Shape.
+  if_option(vertex_shape(ShapeFunction), Options,
+    call(ShapeFunction, V, VShape)
+  ),

-  VAttrs = [label=VLabel].
+  merge_options(
+    [
+      color=VColor,
+      image=VImage,
+      label=VLabel,
+      peripheries=VPeripheries,
+      shape=VShape
+    ],
+    VAttrs
+  ).

diff --git a/gv_gif.pl b/gv_gif.pl
index 4a3e75f..ef2f7f2 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -43,7 +43,7 @@ Support for creating GIF representations.
    ]).
 :- predicate_options(graph_attributes/2, 2, [
      directedness(+boolean),
-     graph_colorscheme(+oneof([none,svg,x11]),
+     graph_colorscheme(+oneof([none,svg,x11])),
      graph_label(+atom)
    ]).

@@ -109,23 +109,23 @@ edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
   if_option(edge_arrowhead(ArrowheadFunction), Options,
     call(ArrowheadFunction, E, EArrowhead)
   ),
-  
   % Color.
   if_option(edge_color(ColorFunction), Options,
     call(ColorFunction, E, EColor)
   ),
-  
   % Label.
   if_option(edge_label(LabelFunction), Options,
     call(LabelFunction, E, ELabel)
   ),
-  
   % Style.
   if_option(edge_style(StyleFunction), Options,
     call(StyleFunction, E, EStyle)
   ),

-  EAttrs = [arrowHead=EArrowhead,color=EColor,label=ELabel,style=EStyle].
+  merge_options(
+    [arrowHead=EArrowhead,color=EColor,label=ELabel,style=EStyle],
+    EAttrs
+  ).


 %! graph_attributes(
@@ -146,10 +146,8 @@ edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
 graph_attributes(GAttrs, Options):-
   % Directedness.
   option(directedness(Directedness), Options, false),
-  
   % Colorscheme.
   if_option(graph_colorscheme(Colorscheme), Options, true),
-  
   % Label.
   if_option(graph_label(GLabel), Options, true),

@@ -169,9 +167,6 @@ graph_attributes(GAttrs, Options):-
 %   * =|vertex_color(+ColorFunction)|=
 %     A function that assigns colors to vertices.
 %     No default.
-%   * =|vertex_coordinate(+CoordinateFunction)|=
-%     A function that assigns coordinates to vertices.
-%     No default.
 %   * =|vertex_image(+ImageFunction)|=
 %     A function that assinges images to vertices.
 %     No default.
@@ -192,27 +187,18 @@ vertex_term(Vs, V, vertex(Id,V,VAttrs), Options):-
   if_option(vertex_color(ColorFunction), Options,
     call(ColorFunction, V, VColor)
   ),
-  
-  % Coordinates.
-  %%%%if_option(vertex_coordinate(CoordinateFunction), Options,
-  %%%%  call(CoordinateFunction, V, VCoordinates)
-  %%%%),
-  
   % Image.
   if_option(image(ImageFunction), Options,
     call(ImageFunction, V, VImage)
   ),
-  
   % Label.
   if_option(vertex_label(LabelFunction), Options,
     call(LabelFunction, V, VLabel)
   ),
-  
   % Peripheries.
   if_option(vertex_peripheries(PeripheriesFunction), Options,
     call(PeripheriesFunction, V, VPeripheries)
   ),
-  
   % Shape.
   if_option(vertex_shape(ShapeFunction), Options,
     call(ShapeFunction, V, VShape)

diff --git a/gv_gif.pl b/gv_gif.pl
index ef2f7f2..6d78ac3 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -40,6 +40,10 @@ Support for creating GIF representations.
      pass_to(vertex_term/3, 3)
    ]).
 :- predicate_options(edge_term/3, 3, [
+     edge_arrowhead(+atom),
+     edge_color(+atom),
+     edge_label(+atom),
+     edge_style(+atom)
    ]).
 :- predicate_options(graph_attributes/2, 2, [
      directedness(+boolean),

diff --git a/gv_file.pl b/gv_file.pl
index 98cb0a2..25b0cd3 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -110,18 +110,14 @@ and GraphViz output files or SVG DOM structures.

 codes_to_gv_file(Codes, ToFile, Options):-
   access_file(ToFile, write),
+  absolute_file_name(data(tmp), TmpFile, [access(write),file_type(dot)]),
   setup_call_cleanup(
-    new_memory_file(MemFile),
-    (
-      setup_call_cleanup(
-        open(MemFile, write, Write, [encoding(utf8),type(test)]),
-        put_codes(Write, Codes),
-        close(Write)
-      ),
-      file_to_gv(MemFile, ToFile, Options)
-    ),
-    free_memory_file(MemFile)
-  ).
+    open(TmpFile, write, Write, [encoding(utf8)]),
+    put_codes(Write, Codes),
+    close(Write)
+  ),
+  file_to_gv(TmpFile, ToFile, Options),
+  delete_file(TmpFile).


 %! file_to_gv(+FromFile:atom, +Options:list(nvpair)) is det.
@@ -137,9 +133,6 @@ file_to_gv(FromFile, ToFile, Options):-
   option(to_file_type(dot), Options), !,
   rename_file(FromFile, ToFile).
 file_to_gv(FromFile, ToFile, Options):-
-  % The input file must be readable.
-  access_file(FromFile, read),
-
   % The method option.
   option(method(Method), Options, dot),
   must_be(oneof([dot,sfdp]), Method),
diff --git a/gv_gif.pl b/gv_gif.pl
index 6d78ac3..e3a6933 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -84,10 +84,10 @@ create_gif(Es, Gif, Options):-
 create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
   % Vertex terms.
   maplist(\V^VTerm^vertex_term(Vs, V, VTerm, Options), Vs, VTerms),
-  
+
   % Edge terms.
   maplist(\E^ETerm^edge_term(Vs, E, ETerm, Options), Es, ETerms),
-  
+
   % Graph attributes.
   graph_attributes(GAttrs, Options).

@@ -104,11 +104,11 @@ create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
 %   * =|edge_label(+atom)|=
 %   * =|edge_style(+atom)|=

-edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
+edge_term(Vs, E, edge(FromId,ToId,EAttrs), Options):-
   edge_components(E, FromV, ToV),
   nth0chk(FromId, Vs, FromV),
   nth0chk(ToId, Vs, ToV),
-  
+
   % Arrowhead
   if_option(edge_arrowhead(ArrowheadFunction), Options,
     call(ArrowheadFunction, E, EArrowhead)
@@ -125,9 +125,9 @@ edge_term(Vs, E, edge(FromId,ToId,EAttrs), _):-
   if_option(edge_style(StyleFunction), Options,
     call(StyleFunction, E, EStyle)
   ),
-  
+
   merge_options(
-    [arrowHead=EArrowhead,color=EColor,label=ELabel,style=EStyle],
+    [arrowhead=EArrowhead,color=EColor,label=ELabel,style=EStyle],
     EAttrs
   ).

@@ -154,7 +154,7 @@ graph_attributes(GAttrs, Options):-
   if_option(graph_colorscheme(Colorscheme), Options, true),
   % Label.
   if_option(graph_label(GLabel), Options, true),
-  
+
   merge_options(
     [colorscheme=Colorscheme,directedness=Directedness,label=GLabel],
     GAttrs
@@ -186,7 +186,7 @@ graph_attributes(GAttrs, Options):-

 vertex_term(Vs, V, vertex(Id,V,VAttrs), Options):-
   nth0chk(Id, Vs, V),
-  
+
   % Color.
   if_option(vertex_color(ColorFunction), Options,
     call(ColorFunction, V, VColor)
@@ -207,7 +207,7 @@ vertex_term(Vs, V, vertex(Id,V,VAttrs), Options):-
   if_option(vertex_shape(ShapeFunction), Options,
     call(ShapeFunction, V, VShape)
   ),
-  
+
   merge_options(
     [
       color=VColor,

diff --git a/gv_file.pl b/gv_file.pl
index 25b0cd3..2d2ed12 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -146,11 +146,8 @@ file_to_gv(FromFile, ToFile, Options):-
   (
     var(ToFile)
   ->
-    absolute_file_name(
-      data(export),
-      ToFile,
-      [access(write),file_type(ToFileType)]
-    )
+    user:prolog_file_type(ToExtension, ToFileType),
+    file_alternative(FromFile, _, _, ToExtension, ToFile)
   ;
     is_absolute_file_name(ToFile),
     % The given output file must match a certain file extension.

diff --git a/gv_file.pl b/gv_file.pl
index 2d2ed12..9eaf66b 100644
--- a/gv_file.pl
+++ b/gv_file.pl
@@ -28,20 +28,16 @@ and GraphViz output files or SVG DOM structures.
 @version 2011-2013/09, 2013/11-2014/01, 2014/05, 2014/07
 */

-:- use_module(library(memfile)).
 :- use_module(library(option)).
 :- use_module(library(process)).
 :- use_module(library(predicate_options)). % Declarations.

 :- use_module(generics(codes_ext)).
 :- use_module(generics(db_ext)).
-:- use_module(generics(error_ext)).
-:- use_module(generics(trees)).
 :- use_module(os(file_ext)).
 :- use_module(os(run_ext)).
 :- use_module(os(safe_file)).
 :- use_module(svg(svg_file)).
-:- use_module(ugraph(ugraph_export)).

 :- use_module(plGraphViz(gv_dot)).

diff --git a/gv_gif.pl b/gv_gif.pl
index e3a6933..48ecd2f 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -27,7 +27,7 @@ Support for creating GIF representations.

 :- use_module(generics(list_ext)).
 :- use_module(generics(option_ext)).
-:- use_module(graph_theory(graph_generic)).
+:- use_module(graph_theory(graph_theory)).

 :- use_module(plRdf(rdf_name)). % Meta-DCG.

diff --git a/gv_gif.pl b/gv_gif.pl
index 48ecd2f..2fad4c4 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -105,7 +105,7 @@ create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
 %   * =|edge_style(+atom)|=

 edge_term(Vs, E, edge(FromId,ToId,EAttrs), Options):-
-  edge_components(E, FromV, ToV),
+  edge(E, FromV, ToV),
   nth0chk(FromId, Vs, FromV),
   nth0chk(ToId, Vs, ToV),

diff --git a/gv_gif.pl b/gv_gif.pl
index 2fad4c4..48ecd2f 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -105,7 +105,7 @@ create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
 %   * =|edge_style(+atom)|=

 edge_term(Vs, E, edge(FromId,ToId,EAttrs), Options):-
-  edge(E, FromV, ToV),
+  edge_components(E, FromV, ToV),
   nth0chk(FromId, Vs, FromV),
   nth0chk(ToId, Vs, ToV),

diff --git a/gv_gif.pl b/gv_gif.pl
index 48ecd2f..d59e5f8 100644
--- a/gv_gif.pl
+++ b/gv_gif.pl
@@ -65,7 +65,7 @@ Support for creating GIF representations.
 %! create_gif(+Edges:ordset, -Gif:compound, +Options:list(nvpair)) is det.

 create_gif(Es, Gif, Options):-
-  edges_to_vertices(Es, Vs),
+  graph_theory:edges_to_vertices(Es, Vs),
   create_gif(Vs, Es, Gif, Options).

 %! create_gif(
@@ -105,7 +105,7 @@ create_gif(Vs, Es, graph(VTerms,ETerms,GAttrs), Options):-
 %   * =|edge_style(+atom)|=

 edge_term(Vs, E, edge(FromId,ToId,EAttrs), Options):-
-  edge_components(E, FromV, ToV),
+  graph_theory:edge_components(E, FromV, ToV),
   nth0chk(FromId, Vs, FromV),
   nth0chk(ToId, Vs, ToV),